The present invention relates to a system for controlling the injection of fuel for a two-cycle engine with a direct fuel injection system wherein fuel is injected together with compressed air in the form of an air-fuel mixture.
There are various methods for supplying fuel to the two-cycle engine. In a method where fuel is mixed with air to make a combustible mixture and the mixture is supplied to a cylinder of the engine, a part of the fuel escapes from the cylinder through an exhaust port upon the scavenging of the cylinder. In order to prevent fuel from escaping through the exhaust port, a method in which air alone is delivered to the cylinder and fuel is injected directly to the cylinder by an injector is proposed. Since the fuel injection occurs during the compression stroke, the fuel must be injected at a high pressure. Accordingly, there has been proposed a fuel injection system where fuel is injected together with compressed assist air.
Japanese Patent Application Laid-Open 60-501963 (International Publication No. WO 85/00854) discloses a fuel injection system where a predetermined amount of fuel is accumulated in a chamber formed in an injector and injected by compressed assist air having a pressure higher than a pressure in the combustion chamber.
However, the assist air inevitably enters the combustion chamber with the fuel. Since the quantity of fuel in a low engine speed range and a light load range is small, the ratio of the total quantity of the air to the fuel in the cylinder increases, thereby rendering the air-fuel mixture lean.